The present invention generally relates to fuel-fired heating appliances and, in a preferred embodiment thereof, more particularly provides a gas-fired water heater having incorporated therein a specially designed combustion air shutoff system.
Gas-fired- residential and commercial water heaters are generally formed to include a vertical cylindrical water storage tank with a gas burner disposed in a combustion chamber below the tank. The burner is supplied with a fuel gas through a gas supply line, and combustion air through an air inlet flow path providing communication between the exterior of the water heater and the interior of the combustion chamber.
Water heaters of this general type are extremely safe and quite reliable in operation. However, under certain operational conditions the temperature and carbon monoxide levels within the combustion chamber may begin to rise toward undesirable magnitudes. Accordingly, it would be desirable, from an improved overall control standpoint, to incorporate in this type of fuel-fired water heater a system for sensing these operational conditions and responsively terminating the firing of the water heater. It is to this goal that the present invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, fuel-fired heating apparatus is provided which is representatively in the form of a gas-fired water heater and includes a combustion chamber thermally communicatable with a fluid to be heated, and a burner structure associated with the combustion chamber and operative to receive fuel from a source thereof. A wall structure defines a flow path through which combustion air may flow into the combustion chamber for mixture and combustion with fuel received by the burner structure to create hot combustion products within the combustion chamber.
The water heater also incorporates therein a specially designed combustion air shutoff system, operative in response to an increased combustion temperature within the combustion chamber created by a reduction in the quantity of combustion air entering the combustion chamber via the flow path (caused, for example, by a progressive clogging of the flow path), for terminating combustion air supply to the combustion chamber, to thus terminate firing of the burner structure, prior to the creation in the combustion chamber of a predetermined elevated concentration of carbon monoxide therein. Representatively, this predetermined elevated concentration of carbon monoxide is in the range of from about 200 ppm to about 400 ppm by volume.
According to one aspect of the invention in a preferred embodiment thereof, the burner structure is disposed within the combustion chamber, a bottom wall of the combustion chamber is defined by an arrestor plate having a perforated portion defined by a series of flame quenching openings extending through the plate, and the combustion air shutoff system includes a temperature sensing structure extending through the arrestor plate into the interior of the combustion chamber, preferably adjacent the burner structure therein. The temperature sensing structure functions to sense a predetermined, undesirably elevated combustion temperature within the combustion chamber, which may be caused by a reduction in the quantity of air being delivered to the combustion chamber via the flow path, or by burning in the combustion chamber of extraneous flammable vapor which has entered its interior through the arrestor plate flame quenching openings, and responsively activate the balance of the combustion air shutoff system to terminate further air inflow into the combustion chamber.
In accordance with a feature of the invention, the temperature sensing structure includes a collar axially projecting into the combustion chamber, a rod coaxially received in the collar and slidably bearing against a laterally crimped collar area, and a esthetic structure carried by the collar and releasably preventing movement of the rod through the collar into the combustion chamber. An open-topped pan structure is supported beneath the arrestor plate and has a bottom wall opening beneath which a shutoff damper is supported in an open position beneath the bottom pan wall opening. The temperature sensing rod releasably blocks the upward movement of the damper to a closed position in which it covers and blocks the pan wall opening, and a spring structure resiliently biases the damper upwardly toward this closed position.
The damper is representatively disposed within an interior plenum area in the water heater which is communicated with a perforated inlet air pre-filtering section disposed on an exterior sidewall portion of the water heater, the combustion air flow path sequentially extending from this pre-filtering section inwardly through the plenum, the interior of the pan structure, and through the arrestor plate flame quenching openings into the interior of the combustion chamber. When the set point of the esthetic temperature sensing structure is reached within the combustion chamber, the esthetic material melts, thereby permitting the spring to upwardly drive the damper to its closed position while at the same time s driving the rod upwardly through the collar into the combustion chamber interior.
According to another feature of the invention, the geometries of the pre-filter structure and the arrestor plate are correlated in a manner facilitating the aforementioned combustion air shutoff, in response to the presence in the combustion chamber of an undesirably increased temperature during firing of the burner structure due, for example, to a progressive clogging of the combustion air inlet flow path, prior to the creation in the combustion chamber of a predetermined elevated concentration of carbon monoxide. From a broad perspective, this correlation involves the relative sizing of the pre-filter structure and arrestor plate perforations in a manner such that the pre-filter structure does not block all potentially clogging airborne particulate matter from entering the combustion air inlet path, but permits a substantial portion of such airborne matter to come into contact with the pre-filter structure to pass through its perforations, traverse the air inlet flow path within the water heater, and come to rest on the bottom side of the arrestor plate.
Representatively, the pre-filter structure is disposed on an outer sidewall jacket portion of the water heater, and the geometries of the pre-filter structure and the arrestor plate are correlated in a manner such that (1) the ratio of the open area-to-total area percentage of the pre-filter structure to the open area-to-total area percentage of the arrestor plate is in the range of from about 1.2 to about 2.5, and (2) the ratio of the total open area of the pre-filter structure to the total open area of the arrestor plate is in the range of from about 2.5 to about 5.3.
In accordance with another feature of the invention, the water heater is provided with a specially designed bottom jacket pan structure that simplifies the construction and reduces the cost of the water heater. The bottom jacket pan structure is preferably of a one-piece molded plastic construction and has an open top side around which an annular, upwardly opening groove is formed. An annular lower end of the external sidewall jacket of the water heater is received in the pan groove, with a lower end portion of the balance of the water heater being downwardly received in the interior of the pan structure in an illustrated embodiment of the bottom jacket pan structure, various other portions of the water heater are integrally formed thereon, including a series of inlet air pre-filtering perforations, a burner access opening, a drain fitting, and a mounting structure for supporting a manual actuation portion of a piezo igniter structure.
According to a further feature of the present invention, the water heater is provided with a spaced series of perforated pre-filter panels, each representatively of a one piece molded plastic construction, which are releasably snap-fitted into corresponding openings in the outer metal jacket portion of the water heater. At the bottom of the outer frame portion of each panel is an upstanding shield structure positioned inwardly of the frame and defining therewith an open-ended trough at the bottom of the shield structure. In the event that a liquid is splashed into a lower portion of the panel it strikes the shield instead of contacting a bottom end portion of a perforated air inlet skirt portion of the water heater spaced inwardly apart from the panel. Liquid striking the shield drains downwardly along its outer side into the aforementioned trough and falls out of the open ends of the trough.
Projecting outwardly from the inner side of the shield are a horizontally spaced plurality of reinforcing tabs which may be brought into contact with the skirt portion of the water heater to limit undesirable inward deflection a portion of the outer jacket structure that extends along the bottom side of the panel""s associated jacket opening.
While principles of the present invention are illustrated and described herein as being representatively incorporated in a gas-fired lo water heater, it will readily be appreciated by those skilled in this particular art that such principles could also be employed to advantage in other types of fuel-fired heating appliances such as, for example, boilers and other types of fuel-fired water heaters. Additionally, while a particular type of combustion air inlet flow path is representatively illustrated and described herein in conjunction with a water heater, it will also be readily appreciated by those skilled in this art that various other air inlet path and shutoff structure configurations could be utilized, if desired, to carry out the same general principles of the present invention.